US11280864B2 - Method for determining and eliminating time delay between radio frequency pulse and layer selection gradient in a magnetic resonance device - Google Patents

Method for determining and eliminating time delay between radio frequency pulse and layer selection gradient in a magnetic resonance device Download PDF

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US11280864B2
US11280864B2 US16/856,359 US202016856359A US11280864B2 US 11280864 B2 US11280864 B2 US 11280864B2 US 202016856359 A US202016856359 A US 202016856359A US 11280864 B2 US11280864 B2 US 11280864B2
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layer selection
radio frequency
frequency pulse
gradient
time delay
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US20200341086A1 (en
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De He Weng
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Siemens Healthcare GmbH
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/46—NMR spectroscopy
    • G01R33/4625—Processing of acquired signals, e.g. elimination of phase errors, baseline fitting, chemometric analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/56572—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of a gradient magnetic field, e.g. non-linearity of a gradient magnetic field
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
    • G01R33/3852—Gradient amplifiers; means for controlling the application of a gradient magnetic field to the sample, e.g. a gradient signal synthesizer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/543—Control of the operation of the MR system, e.g. setting of acquisition parameters prior to or during MR data acquisition, dynamic shimming, use of one or more scout images for scan plane prescription
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/30—Assessment of water resources

Definitions

  • the disclosure relates to magnetic resonance and, in particular, to a method for determining and eliminating a time delay between a radio frequency pulse and a layer selection gradient in a magnetic resonance device.
  • a magnetic resonance (MR) sequence using radio frequency (RF) pulses and gradients can excite a specific plane, thick layer or voxel. After excitation, all linear phase radio frequency pulses require a re-phase gradient.
  • the synchronization of a radio frequency pulse and a gradient pulse has strict requirements. For example, the center of a full shape radio frequency pulse should occur at the same time as the center of a thin or thick layer selection gradient. However, in reality, it is difficult to satisfy this condition precisely. For example, the gradient is not consistent with the radio frequency pulse in control precision, the switching of the gradient generates eddy current, and the like, which all prevent the condition from being satisfied.
  • the mismatch between the radio frequency pulse and the layer selection gradient can also generate an excitation artifact.
  • the present disclosure proposes a method for determining and eliminating a time delay between a radio frequency pulse and a layer selection gradient in a magnetic resonance device.
  • a method for determining a time delay between a radio frequency pulse and a layer selection gradient in a magnetic resonance device comprising:
  • a read-out encoding gradient is in the first direction
  • a phase encoding gradient is in a second direction
  • the second direction is orthogonal to the first direction
  • ⁇ is the phase of the image in the first direction
  • ⁇ is a gyromagnetic ratio constant
  • G is the magnitude of the layer selection gradient
  • ⁇ is the time delay between the radio frequency pulse and the layer selection gradient
  • z is the position of a point on the image in the first direction
  • z 0 is the position of the center of the image in the first direction.
  • the spatial encoding gradient is of a gradient echo or planar echo encoding mode.
  • a method for eliminating a time delay between a radio frequency pulse and a layer selection gradient in a magnetic resonance device comprising:
  • a read-out encoding gradient is in the first direction
  • a phase encoding gradient is in a second direction
  • the second direction is orthogonal to the first direction
  • ⁇ is the phase of the image in the first direction
  • ⁇ is a gyromagnetic ratio constant
  • G is the magnitude of the layer selection gradient
  • ⁇ is the time delay between the radio frequency pulse and the layer selection gradient
  • z is the position of a point on the image in the first direction
  • z 0 is the position of the center of the image in the first direction.
  • the spatial encoding gradient is of a gradient echo or planar echo encoding mode.
  • the method for determining and eliminating a time delay between a layer selection gradient and a radio frequency pulse in the present disclosure directly measures the time delay between the layer selection gradient and the radio frequency pulse by using phase information. This method is more sensitive and more accurate than existing methods that use signal or artifact strength. In addition, this method requires only one measurement, and is therefore faster than methods that manually adjust some parameters to find the minimum or maximum signal.
  • FIG. 1 is a flowchart of a method for determining a time delay between a layer selection gradient and a radio frequency pulse according to a first embodiment of the present disclosure.
  • FIG. 2 is a sequence diagram of determining a time delay between a layer selection gradient and a radio frequency pulse according to an embodiment of the present disclosure.
  • FIG. 3 is a flowchart of a method for eliminating a time delay between a layer selection gradient and a radio frequency pulse according to a second embodiment of the present disclosure.
  • FIG. 4 illustrates an example magnetic resonance imaging device, in accordance with an embodiment of the present disclosure.
  • FIG. 5 illustrates an example functional structure of a control device of the magnetic resonance imaging device shown in FIG. 4 , in accordance with an embodiment of the present disclosure.
  • FIG. 1 is a flowchart of a method 100 for determining a time delay between a layer selection gradient and a radio frequency pulse according to a first embodiment of the present disclosure.
  • the method 100 includes steps S 102 , S 104 , S 106 , S 108 , and S 110 .
  • step S 102 a radio frequency pulse and a layer selection gradient are provided.
  • FIG. 2 is a sequence diagram of determining a time delay between a layer selection gradient and a radio frequency pulse according to an embodiment of the present disclosure.
  • FIG. 2 shows a linear phase radio frequency pulse and a corresponding layer selection gradient, and the gradient is in a first direction (the Z-axis direction in this embodiment).
  • the method of the present disclosure is not limited to a linear phase radio frequency pulse and a layer selection gradient, and is also applicable in the case of multiple pulses and multiple gradients.
  • the time delay r between the layer selection gradient and the radio frequency pulse is the distance between the center of the radio frequency pulse and a position where the area formed by the right portion on the layer selection gradient and the Z axis is equal to the area formed by a re-phase gradient and the Z axis.
  • step S 104 the radio frequency pulse and the layer selection gradient are applied to an imaging object at the same time.
  • step S 106 data sampling is performed with a spatial encoding gradient, wherein a read-out encoding gradient is in the Z-axis direction, a phase encoding gradient is in a second direction (the Y-axis direction in this example), and the Y-axis direction is orthogonal to the Z-axis direction.
  • the sequence is similar to a normal thin or thick layer selection sequence, except that only the read gradient is moved to the axis where the thin or thick layer selection gradient is located.
  • the spatial-encoding gradient is of a gradient echo or planar echo encoding mode
  • FIG. 2 shows a spatial encoding gradient of the planar echo encoding mode.
  • a phase of an image in the first direction is acquired (e.g., a phase of an image associated with an object being imaged via the magnetic resonance imaging device). Phase information of the image is used to calculate a time delay.
  • the time delay between the radio frequency pulse and the layer selection gradient is determined according to the above formula.
  • ⁇ is a gyromagnetic ratio constant
  • z is the position of a point on the image along the axis where the layer selection gradient is located
  • z 0 is the position of the center of the image along the axis where the layer selection gradient is located.
  • FIG. 3 is a flowchart of a method 200 for eliminating a time delay between a layer selection gradient and a radio frequency pulse according to a second embodiment of the present disclosure.
  • the method 200 includes steps S 202 , S 204 , S 206 , S 208 , S 210 , and S 212 .
  • Steps S 202 , S 204 , S 206 , S 208 and S 210 are respectively identical to steps S 102 , S 104 , S 106 , S 108 and S 110 .
  • step S 212 the time delay between the radio frequency pulse and the layer selection gradient is adjusted to eliminate a phase difference of points on the image in the first direction.
  • the method for determining and eliminating a time delay between a layer selection gradient and a radio frequency pulse in the present disclosure directly measures the time delay between the layer selection gradient and the radio frequency pulse by using phase information. This method is more sensitive and accurate than existing methods that use signal or artifact strength. In addition, this method requires only one measurement, and is therefore faster than methods that manually adjust some parameters to find the minimum or maximum signal.
  • FIG. 4 illustrates an example magnetic resonance imaging device, in accordance with an embodiment of the present disclosure.
  • the magnetic resonance imaging device as shown in FIG. 4 may also be referred to as a magnetic resonance imager or magnetic resonance imaging system.
  • This comprises, as known in principle, a main magnet unit 6 (e.g. a magnetic data acquisition unit or scanner) that defines a patient receiving space 7 into which a patient can be moved by means of a patient support 8 (not shown in further detail here).
  • a high frequency arrangement of the magnetic resonance imaging device 5 and a gradient coil arrangement of the magnetic resonance imaging device can be provided and, for the sake of clarity, these are also not shown.
  • the magnetic resonance imaging apparatus 5 may be controlled by a control device 10 , which may also be referred to as a control computer, control circuitry, of control unit.
  • the control device 10 is configured to communicate with and/or control one or more components of the magnetic resonance imaging device 5 .
  • the control device 5 may do so to perform one or more method according to the present disclosure, such as the method 100 , 200 , for example, as described herein with reference to FIGS. 1 and 3 .
  • the control device 10 may be implemented, for example, as one or more computer processors.
  • the various components of the control device 10 as discussed below may be implemented as separate processors, or their respective functions shared among one or more processors of the control device 10 .
  • the various functions of the components of the control device 10 which are discussed directly below, may be achieved via any suitable combination of one or more hardware processors, software, or a combination of both.
  • FIG. 5 shows the functional structure of the control device 10 .
  • the control device 10 comprises RF pulse and a layer selection gradient circuitry 11 to control the magnetic resonance imaging device 5 to generate RF pulses and layer selection gradients, in this example as discussed in steps S 102 /S 202 of FIGS. 1 and 3 .
  • the control device 10 also includes RF pulse and layer selection gradient circuitry 12 configured to control the magnetic resonance imaging device 5 to apply the RF pulses and layer selection gradients to an object (e.g., a patient) at the same time, in this example as discussed in steps S 104 /S 204 of FIGS. 1 and 3 .
  • the control device 10 also includes data sampling circuitry 13 configured to control the magnetic resonance imaging device 5 to perform data sampling with a spatial encoding gradient, in this example as discussed in steps S 106 /S 206 of FIGS. 1 and 3 . Furthermore, The control device 10 also includes phase acquisition circuitry 14 configured to control the magnetic resonance imaging device 5 to acquire the phase of an image in a first direction, in this example as discussed in steps S 108 /S 208 of FIGS. 1 and 3 .
  • control device 10 includes time delay calculation circuitry 15 configured to calculate a time delay between the radio frequency pulse and the layer selection gradient according to the phase of the image in the first direction, in this example as discussed in steps S 110 /S 210 of FIGS. 1 and 3 .
  • the control device 10 may also comprise time delay adjustment circuitry 16 to control the magnetic resonance imaging device 5 to adjust the time delay between the radio frequency pulse and the layer selection gradient to eliminate a phase difference of points on the image in the first direction, in this example as discussed in step S 212 of FIG. 3 .
  • the control device 10 may further comprise a user interface for receiving information entered by the user, which is not shown in the Figures for purposes of brevity.
  • the control device 10 may also include one or more memories 17 , such as non-transitory computer-readable mediums, for example.
  • the one or more memories 17 may be configured as any suitable type of storage mediums such as volatile or non-volatile storage devices, and may form part of the control device 10 or otherwise be accessed by the control device 10 (e.g., via a network), and thus be external to the control device 10 (not shown).
  • Aspects include any of the methods being performed additionally or alternatively via executable instructions stored in the one or more memories 17 , which may be executed by one or more components of the control device 10 and/or the magnetic resonance imaging device 5 (e.g., via one or more processors).
  • embodiments include machine-readable instruction(s) being stored on the computer-readable storage medium.
  • the machine-readable instruction when executed by one or more processors, may thus cause the one or more processors to perform any one of the methods described above.
  • embodiments include a system or apparatus being equipped with a readable storage medium; software program code realizing a function of any one of the embodiments above may be stored on the readable storage medium, and a computer or processor of the system or apparatus may be caused to read and execute a machine-readable instruction stored in the readable storage medium.
  • program code read from the readable storage medium may itself realize a function of any one of the embodiments above, hence machine-readable code and the readable storage medium storing the machine-readable code form part of the present disclosure.
  • Examples of readable storage media include floppy disks, hard disks, magneto-optical disks, optical disks (such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD+RW), magnetic tapes, non-volatile memory cards and ROM.
  • program code may be downloaded (e.g. from a server computer or a cloud) via a suitable communication network.

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  • Condensed Matter Physics & Semiconductors (AREA)
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CN111830450B (zh) * 2019-04-23 2023-08-04 西门子(深圳)磁共振有限公司 确定和消除磁共振设备中射频脉冲与选层梯度之间的时延的方法
CN114325531A (zh) * 2021-12-31 2022-04-12 深圳市联影高端医疗装备创新研究院 磁共振系统延迟的校正方法、装置、计算机设备和介质

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CN111830450B (zh) * 2019-04-23 2023-08-04 西门子(深圳)磁共振有限公司 确定和消除磁共振设备中射频脉冲与选层梯度之间的时延的方法
CN110118950B (zh) * 2019-06-19 2021-01-01 华东师范大学 一种腹部定量磁化率成像中双极读出梯度的相位校正方法

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